Designer elements

To start with some corrections to my previous post about nanotechnology: First, it was not George Smalley but William Shockley, one of the inventors of the transistor in 1947, who made the "amplification" analogy about the bale of hay attached to the mule's tail.

Second, I'm still struggling with the concept of the location of an unlocatable electron. The truth, it seems, is that the electron does very much have a position, but in the odd sense that there is a wave function describing its location at any particular time as a varying probability. (Just as a sine-wave-ish function describing a water wave has an amplitude that corresponds to the height of the water, a Schroedinger wave function describes the probability of an election being somewhere at a particular time.) That is, it may not be in our power to pinpoint where an electron is at any particular moment, but there are many areas where the electron is so unlikely to be that you can pretty much ignore the possibility. The areas of likely location may be more or less confined and comprehensible, such as the surface of a rather small, fuzzy sphere in an identifiable neighborhood.

On to more wonders about nanotechnology: I was surprised to read that all atoms, from tiny one-proton hydrogen to obese, unwieldy uranium with its 92 protons (we can ignore larger atoms, which are too unstable to stay together long), are roughly a tenth of a nanometer in diameter. Despite the difference in the size of their nuclei, all the atoms in the periodic table have an effective "size" that corresponds to the cloud formed by the outer layer of their electrons. The negatively charged electrons are all being sucked into toward the nucleus by their electrical attraction to the positive protons, but at the same time the electrons are fiercely repelling each other, so they stand off from the nucleus in the stable positions permitted by the mysterious laws of quantum mechanics. (The protons in the nucleus try to repel each other, too, but there's an attraction between protons called the "strong nuclear force" that, at extremely short distances, vastly overwhelms the repulsive electric force.) For whatever reason, the stable positions for the outermost orbiting electrons are pretty close to the same distance from the nucleus no matter how many of them are packed in below; there's an awful lot of empty space in there, and a very powerful electrical attraction keeping things tight.

It's the outer layer of electrons that concerns us most in daily life. Just about everything we normally experience as the properties of atoms has to do with their outer shell of electrons; that's where the phenomena of chemical bonding and the absorption or reflection of light mostly take place. That's one reason elements in the same column of the periodic table have such similar properties: the difference in atomic weight and number is often less important than the similarity in outer electron shells.

That brings us to artificial atoms. According to this terrific Wired article from several years ago, when we manufacture quantum dots, their electron clouds act a lot like ordinary atoms, despite their hollow cores.  For instance, they can make pseudo-chemical bonds just as the electrons in normal atoms do. But artificial atoms need not simply mimic elements number 1-92 on the periodic table. Their electron shells don't necessarily have to be roughly spherical, as those of natural atoms are, because we are shaping them with a variety of forces that need not be as simple as the radially symmetric pull of a nucleus. That means that there may be bazillions of artificial atoms available to us, each with its own chemical and spectral behavior. What's more, we may be able, by doing something as simple as altering the shaping magnetic field, to alter the electron shell and therefore transmute one artificial element instantaneously into another.

8 comments:

Grim said...

Lead into gold, more or less. The secret to the Philosopher's Stone was to do away with the essence (insofar as an element is defined essentially by that which is represented by the atomic number) and focus on the accidents (i.e., the shape of the cloud).

Isaac Newton would be so happy. Alchemy was his real love.

Texan99 said...

But also, the mysterious foil-thin spaceship hull materials of the Galactic Overloads, which can't be cut with any tools we have, but can be made to open doors and windows at will. Or smart fabrics that make a barrier to heat, light, and moisture in either direction depending on need, or change from flexible to brittle depending on whether we want to touch our toes or stop a bullet.

Grim said...

Sounds nice. What's the power consumption like for maintaining a Hull of the Galactic Overloards? Any estimates?

Texan99 said...

Tiny. These are energy inputs only big enough to jump a tiny atomic gap, remember? Kind of like the bit of current that turns clear glass cloudy in one of those cool conference-room windows. It doesn't take a lot of brute force to encourage electrons to pack differently, only perhaps a tiny change in the magnetic field around them, but the macro-scale impacts are huge.

Grim said...

OK for reconfiguring, but what about holding all those designer 'elements' in place to begin with? You're doing something to keep those electrons from flying apart, something more or less simulating the function of the nucleus. What does that cost?

Texan99 said...

Apparently very little. Having a nucleus handy is not the only way to introduce a bit of positive charge to control the shape of an electron cloud. To give an idea of the scale of things, the addition of 0.001% of arsenic (as an N-type "dopant") donates an extra 10^17 free electrons in a cubic centimeter of silicon and the electrical conductivity is increased by a factor of 10,000. I assume the same scale of effect is achieved by adding a P-type dopant that decreases the level of free electrons and creates positively-charged "holes." Or you can shape an electron cloud with a tiny magnetic field. There's a huge leverage there: a little bit of electric force to shape an electron cloud produces a change of geometry that has enormous implications on the macro scale by influencing the kind of chemical combination that takes place.

Graduate students create these nano-structures on their desktops. They don't need huge particle accelerators or nuclear plants or anything to pull it off. They're using positive and negative electrical forces already present in ordinary, plentiful ions.

Electric charges are terrifically strong. We don't always notice that, because under normal circumstances they're almost perfectly balanced, positive against negative. The most minor imbalance creates forces that seem huge to us on the human scale.

Grim said...

Fascinating. For many years I've been hearing engineers suggest that the primary concern was power. But perhaps that's wrong -- perhaps we can manage the power issues, if we can learn how to do it subtly enough.

douglas said...

Grim, how much power does it take to hold a rock together? Now, getting a door to open in it might require a little more- or only enough to induce a reversible 'phase' change of some kind (I don't think that's really the correct term, but whatever property change that allows a door to open in an otherwise rigid material) which if it's through these means, again, very little. A watch battery could do it for a considerable length of time.